1. Field of the Invention
This invention relates to an apparatus for and a method of manufacturing an optical disc typified by a so-called DVD disc or a blue-ray disc. More particularly, it relates to an apparatus for and a method of manufacturing an optical disc more suitable when manufacturing an optical disc of a type having two recording layers on one surface thereof.
2. Related Background Art
For example, a blue-ray disc which is an optical recording medium called an optical disc is comprised of a substrate comprising polycarbonate or the like having a groove and a pit formed on the surface thereof, a sputter layer comprising a reflecting layer, a recording layer, etc. for example, by a sputtering method formed on the upper surface of the groove or the like, a light transmitting layer covering the upper surface of the sputter layer, and a protective layer covering the surface of the substrate. Also, there has been proposed a disc having a plurality of recording layers in order to further heighten a recording capacity, and in this disc, a spacer layer is formed on the upper surface of a sputter layer, and a groove and a pit are formed on the upper surface of the spacer layer. The above-mentioned sputter layer, etc. are further successively formed on the upper surface of the groove, etc. to thereby obtain a plurality of recording layers, and a further increase in the recording capacity is contrived.
When the above-described blue-ray disc is to be manufactured, the light transmitting layer and the spacer layer are obtained by sticking a viscous sheet, or by hardening a layer of resin or the like formed by a spin coat method. Both of these two methods have various characteristics, but when cost and productivity are taken into consideration, the spin coat method is considered to be practically more suitable. In this case, the groove, etc. on the spacer layer are obtained by pressure-sticking a stamper formed with a negative pattern in advance on the surface of the resin layer keeping fluidity, transferring this pattern, and thereafter stripping off the stamper form the surface of the resin layer.
At the stamper stripping-off step, heretofore, the stamper has been held by a jig, and a force has simply been applied in a direction perpendicular to the extension surface of the spacer to thereby strip off the stamper from the surface of the spacer (see, for example, Japanese Patent Application Laid-Open No. 2001-126322 A). In this method, however, there is the possibility of damaging not only the stamper, but also the spacer layer or the substrate, and in case of stripping-off, the application of a very great force has been required. Therefore, from the viewpoint of reducing the force required for stripping-off and starting smooth stripping-off, there has been proposed, for example, a method of forcibly forming cut-in in an aperture at the center of the disc, and inserting compressed air through a gap formed by partial stripping-off to thereby effect stripping-off.
Also, the inventor has proposed, as a method of executing the stripping-off step more smoothly and easily, a method of making the stamper layer than the surface of the substrate, and executing the stripping-off step by the use of that portion of the stamper which protrudes from the upper surface of the substrate (see, for example, Japanese Patent Application Laid-open No. 2003-326535 A). In this method, in a state in which the substrate is fixed, the protruding portion is pressed in a direction away from the substrate by a plurality of pins, and when the pins press the substrate, the respective pins effect pressing along the outer periphery of the substrate with a time difference provided among them. By the addition of such a construction, the ease of stripping-off and a reduction in a load given to the stamper, etc. during the stripping-off are contrived.
The optical disc which is a recording medium, along with an improvement in recording density, is required to become narrow in the width of the groove transferred to the spacer layer, and reliably transfer the groove shape. Thus, the stamper used for the transferring of the groove has a groove pattern which is minute and high in accuracy of formation, and the cost required for the working of the stamper itself is rising. Also, an ultraviolet ray or the like is applied to the spacer layer through the stamper to thereby carry out the hardening of this layer and therefore, the stamper is required to have sufficient thinness to transmit the ultraviolet ray therethrough and not to attenuate the intensity of the ultraviolet ray.
However, when the stripping-off of the stamper is effected by pushing up the vicinity of the outer periphery of the stamper from the surface of the substrate by the pins, the concentration of a load occurs to the contact portion between the pins and the stamper. Also, the frictional force between the tip ends of the pins and the contact surface of the stamper occurring to the contact portion is great. Therefore, there remains the possibility of damaging the stamper. Thus, it is necessary to disuse the expensive stamper after a relatively small number of times of use, and use a new stamper. Also, when the stamper is made into a thin layer having a thickness of e.g. 0.6 mm, there is the undesirable possibility that such a construction cannot cope with the thin-layer stamper.